Epoxy compounds are compounds widely used in the fields of organic chemistry and polymer chemistry. The compounds are useful in a variety of fields for industrial application, such as fine chemicals, raw materials of drugs, agrochemicals, and resins as well as electronic information materials and optical materials.
Further, when multi-functional epoxy compounds are cured with various hardeners, products thus cured are generally excellent in mechanical characteristics, water resistance, chemical resistance, heat resistance and electrical characteristics, and utilized in a broad range of fields as adhesives, paints, laminates, composite materials, and the like. In particular, glycidyl amine-type epoxy compounds are low in viscosity and excellent in heat resistance, and accordingly the usage thereof for composite materials and electronic materials is increased. Particularly, N,N,N′,N′-tetraglycidyl-diaminodiphenyl ethers are useful raw materials for epoxy resins as fiber-reinforced composite materials (see, for example, Japanese Unexamined Patent Publication Kokai Nos. Hei 03-26750 and 04-335018). Epoxy compounds mainly containing N,N,N′,N′-tetraglycidyl-diaminodiphenyl ethers are demanded to have a high purity for improving the performance of fiber-reinforced composite materials and also to have a low viscosity for suitable molding processability.
Conventionally, as a method for producing a glycidyl amine-type epoxy compound, there has been proposed a method in which a diamine is reacted with an epihalohydrin at a reaction temperature of less than 60° C. in the presence of 0.5 to 15 moles of water relative to 1 mole of the raw-material diamine (Japanese Examined Patent Publication No. Sho 61-6828). Moreover, as a method for producing N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl ether, there has been proposed a method in which 4,4′-diaminodiphenyl ether is reacted with epichlorohydrin at a reaction temperature of 60° C. within a reaction period of 12 hours in a solvent of N,N-dimethylformamide or N,N-dimethylacetamide, which are polar aprotic solvents with a high boiling point (see, for example, Journal of Applied Polymer Science, Vol. 77, 2430-2436 (2000) and European Polymer Journal, Vol. 31, No. 4, pp. 313-320 (1995)). However, if that production method is employed for N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether, resultant N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether contains a large amount of impurities and has a high viscosity. This is attributable to a large difference between the reactivity of the amino group at the 3-position of raw-material 3,4′-diaminodiphenyl ether and the reactivity of the amino group at the 4-position of 4,4′-diaminodiphenyl ether.
Moreover, as a method for producing N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether, it is stated that 3,4′-diaminodiphenyl ether is reacted with epichlorohydrin in a solvent mixture of benzene and acetic acid at a reaction temperature of 60° C. for 14 hours (International Patent Publication No. 97/13745). However, in that production method, when reacted with 3,4′-diaminodiphenyl ether, epichlorohydrin is simultaneously reacted with acetic acid. This brings about problems that a large amount of by-products are generated, and that N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether thus obtained has a high viscosity.
In other words, when synthesized by the conventional methods, N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether thus obtained contains a large amount of impurities in diglycidyl, triglycidyl, and chlorohydroxypropyl forms. These are highly reactive and react with the target product N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether, bringing about a problem of lowering the quality. To put it differently, active hydrogens of the impurities in diglycidyl, triglycidyl, and chlorohydroxypropyl forms react with the target product N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether, and gradually increase the viscosity. In addition, N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether synthesized by the conventional methods contains a large amount of oligomers generated by reaction between an intermediate, N,N,N′,N′-tetrakis(3-chloro-2-hydroxypropyl)-3,4′-diaminodiphenyl ether, formed in the production process and epichlorohydrin remaining in the system. This also causes the viscosity to be increased.
Particularly, when used as the raw material of an epoxy resin, N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether with a high viscosity does not mix well with a hardener and an additive that are other components constituting the epoxy resin composition. This makes it difficult to obtain a uniform composition. Further, heating to obtain a uniform composition, however, results in disuniformity attributable to the aforementioned impurities in the diglycidyl, triglycidyl, and chlorohydroxypropyl forms. As a result, the resultant epoxy resin hardly has physical properties expected from the reaction between N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether and the hardener.
Additionally, both of low-purity N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether obtained by the conventional production methods and impurities contained therein have high boiling points. Accordingly, when the impurities are separated and removed by a method such as purification through distillation so as to increase the chemical purity, the distillation has to be performed at high temperature. This brings about a problem that the purity or the yield is lowered during the distillation. As described above, an industrially usable epoxy compound of high-purity N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether has yet to be produced.
It could therefore be helpful to provide an epoxy compound of high-purity N,N,N′,N′-tetraglycidyl-3,4′-diaminodiphenyl ether and a method for producing the same.